The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization of the MR element, which in turn causes a change in resistance of the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the GMR sensor varies as a function of the spin-dependent transmission of the conduction electrons between ferromagnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the ferromagnetic and non-magnetic layers and within the ferromagnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer (reference layer), has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO or Fe—Mn) layer. The pinning field generated by the antiferromagnetic layer should be greater than demagnetizing fields (about 200 Oe) at the operating temperature of the SV sensor (about 120° C.) to ensure that the magnetization direction of the pinned layer remains fixed during the application of external fields (e.g., fields from bits recorded on the disk). The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field).
One well known way to increase the performance of magnetic disk drives is to increase the areal data storage density of the magnetic hard disk. This can be accomplished by reducing the written data track width, such that more tracks per inch can be written on the disk. To read data from a disk with a reduced track width, it is also necessary to develop sufficiently narrow read head components, such that unwanted magnetic field interference from adjacent data tracks is substantially eliminated.
Thin film head components such as sensors are created by wafer processing. Typically, a layer of photoresist is added to define the width of the component positioned underneath, and exposed material is removed by various processes. As components become smaller the lithographic patterns must also become smaller yet must maintain a high resolution to properly form the components.
Shrinking thin-film head (TFH) device geometries force adoption of more advanced lithography platforms for enhanced resolution of small features. Products planned for the near-term future exceed the printing capability of the existing manufacturing platform, deep-ultraviolet (DUV, 248 nm wavelength) lithography. The 193 nm wavelength lithography platform provides extended resolving capability, but poses challenges in integration of the lithographic patterns into the TFH read-head build process.
One difficulty is that 193 nm photoresists tend to have poor etch resistance. If reactive ion etching (RIE) is used, the topography of the photoresist pattern tends to be destroyed because the photoresist etches away along with the underlayer. If edges of the photoresist are reduced, i.e., the resolution is degraded, the edges of the component will be removed, resulting in a deformed component. Further, if too little photoresist remains, the photoresist will tend to become encapsulated by subsequently deposited materials, making liftoff difficult or impossible. FIG. 1 illustrates a read head 100 just before liftoff according to a standard photolithography process. As shown, the photoresist 102 becomes shrunken and rounded from the RIE, resulting in the deposited material 104 encasing the remaining resist structure completely. The solvent cannot reach the photoresist 102 to effect the liftoff.
Prior art attempts to overcome the problem of photoresist erosion used thicker layers of photoresist. However, the photoresist tended to fall over during subsequent processing. For typical photoresists, only an aspect ratio of about 3 to 1 photoresist height/width or less is stable enough for further processing.
Yet another problem is the need for a bottom antireflective coating (BARC) to suppress standing waves and sensitivity of the photoresist's printed linewidth to fluctuations in photoresist thickness. Most BARC materials are insoluble in wet stripping reagents, complicating rework of the photoresist pattern.
Electron-beam (e-beam) lithography provides an alternative platform for extended resolving capability, but it lags behind the optical platforms in readiness and is generally less cost-effective due to low tool throughput.